Reversibly extensible film

ABSTRACT

A reversibly extensible polymeric film is hot formed, as by coextrusion, using selected polymeric materials that provide discrete areas of elastic and inelastic polymeric materials arranged in laterally spaced and longitudinally elongated lanes or stripes connected by integrally formed joints therebetween. The elastic materials comprise block polymers selected from tetrablock, triblock and diblock polymers, and the inelastic material is selected from polyolefins such as polyethylene, polypropylene, poly(ethylene-propylene), poly(ethylene-vinyl acetate), poly(styrene-butadiene), or copolymers or blends thereof.

BACKGROUND OF THE INVENTION AND RELATED ART

The present invention relates to flexible sheet or roll stock filmhaving elastic characteristics and to products formed of such film.Film-forming polymers are used to hot form the film with elastic andnonelastic or inelastic discrete polymer portions connected at a jointtherebetween.

The films are useful in tapes, closure devices, labels and otherconstructions requiring a stretchable or elastic film element. The shearresistance and elastic property of the film in combination with thenon-creep nature of the inelastic portions provide unique and valuableperformance useful in a wide range of applications. The films may beused as a construction film for forming an element of a morecomprehensive tape or closure system including industrial or craftapplications requiring pieces to be secured together with tension duringa dry cycle or medical applications such as medical tapes, suture tapes,nasal dilators, bandages and the like.

The films are particularly useful as substrates for closure systems suchas mechanical and/or self-adhesive diaper fastening tapes or tabs. Insuch applications, the elastic characteristic of the film enhances fit,comfort, absorbency, containment and/or security of closure. The filmsmay also be used as attachments to the waist or leg areas of a device orarticle of clothing for enhancing fit, comfort, and/or sealingcharacteristics. The film is especially useful in connection withdisposable diaper tape fastening systems, and it is specificallydescribed with respect to the same hereinafter.

Disposable diapers are known in the art and comprise multiple layerassemblies or laminates including an inner filling of absorbent fiber ormaterial sandwiched between outer layers. One of the outer layersincludes an absorbent material to be disposed against the user, and theother outer layer may comprise a waterproof plastic film for containmentof waste within the diaper.

The use of stretchable fastening tapes or tabs in disposable diapers isdisclosed in U.S. Pat. No. 3,800,796 to Jacobs. In Jacobs, a polymericvariation of the tape includes a semielastic strip having a fullyextensible elastic central segment and two non-extensible inelasticterminal segments. The elastic segment comprises a heat-sealableelastomer such as a butadiene-styrene block polymer. The patent does notdescribe a coextrusion process for making film that may be used to formthe tape.

U.S. Pat. No. 4,787,897 to Torimae et al. discloses a co-extruded diaperfastening tape with an elastic central segment and nonelastic terminalsegments. The elastic segment includes triblock polymers containing 10to 80 parts of a processing aid comprising a hydrogenated terpene resinor alicyclic hydrocarbon having a melt or softening point of 80° C. anda molecular weight of 400 to 2000.

SUMMARY OF THE INVENTION

It has now been discovered that certain polymeric materials comprisingthermoplastic elastomers may be used to form reversibly extensiblesheets or roll film material. The sheets or films include discreteportions of thermoplastic elastomer having elastic characteristicsjoined with portions of thermoplastic polymer having nonelasticproperties.

The thermoplastic elastomers and the thermoplastic polymers arefilm-forming polymers that may be hot formed as by simultaneouscoextrusion. For example, the film-forming polymers may be co-extrudedin a pattern of laterally spaced and longitudinally parallel polymerlanes or stripes extending in the machine direction with integrallyformed joints adhering adjacent lanes together.

The film material according to the invention has excellent extrusioncharacteristics and superior joint strength between the elastic and thenonelastic polymers. Also, the film materials have improved elevatedtemperature shear properties and improved caliper and roll conformationas indicated by wound rolls of near cylindrical configuration.

The thermoplastic polymer may be a polyolefin such as polyethylene,polypropylene, poly(ethylene-propylene), poly(ethylene-vinyl acetate),poly(styrene-butadiene), or copolymers or blends thereof. A minor amountof an ethylene-propylene component may be incorporated in thethermoplastic polymer. Polypropylene is a preferred thermoplasticpolymer. Films of such polymers, e.g. 0.1 to 20 mils thick, exhibitlittle or no recovery from stretching or deformation and exemplify theinelastic or nonelastic properties of interest herein.

Thermoplastic elastomers of interest herein are block copolymers havingor containing the tetrablock structure A-B-A-D, the triblock structureA-B-A and, optionally, the diblock structure A-B in lesser amounts as aminor component. In such block structures, A represents a block which isnon-rubbery or glassy or crystalline at service temperature, e.g. about100° F. in the case of diaper tapes, and B and D, which may be the same,each represent a block which is rubbery or elastomeric at servicetemperature. At elevated temperatures, the A, B and D blocks aresufficiently fluid to enable coextrusion of the thermoplastic elastomer.Films of such polymers, e.g. 0.1 to 20 mils thick, exhibit recovery fromstretching or deformation below their yield point and exemplify theelastic properties of interest herein.

The thermoplastic elastomer may be blended with a thermoplastic polymerend block reinforcing agent of relatively high molecular weight, e.g. amolecular weight greater than 2000 and, more preferably, in the range of3000 to 5000, and higher. Such reinforcing agents improve elevatedtemperature shear strength. Most unexpectedly, such reinforcing agentshave been found herein to increase the caliper or gauge uniformity ofwide sheet coextrusions, e.g. 1500 mm or 60 inches.

Preferred reinforcing agents are high molecular weight aromaticcompounds such as polyphenylene oxide (or polyphenyl ether) which havemolecular weights in the range of 3,000 to 30,000 and higher. Thesereinforcing agents are added in amounts ranging from 3 to 9, and morepreferably, from 8 to 9 parts by weight based on the weight of theelastomer component. Other preferred reinforcing agents comprise puremonomer resins of polycyclic arenes including substituted andunsubstituted vinylarenes such as styrene and methylstyrene. These areused in amounts ranging from 5 to 25, and more preferably, from 12 to 14parts by weight based on the weight of the elastomer component.

Other conventional additives such as antioxidants, colorants andprocessing aids may be added to either or both the elastic andnonelastic polymers.

A diaper fastening tape should have the ability to withstand an appliedload of 500 grams for more than 1,000 minutes at 100° F. (100° F. beingused to simulate body temperature.) Some of the films in accordance withthe invention have shear strengths that exceed 10,000 minutes at 100° F.under a 5 g load.

The reason for the improved shear strength is believed to be related tothe unique nature of the joint at the joining plane or interface wherethe thermoplastic meets the tetrablock thermoplastic elastomer. Thestrength of the joint is believed to be improved by the uniqueinteraction of the saturated tetrablock elastomer with the thermoplasticpolymer. More particularly, preferred tetrablock elastomers include aterminal segment or free tail block of ethylene-propylene that providesa hydrocarbon structure similar to the hydrocarbon groups of thethermoplastic so as to favor interaction and improved joint strength.This effect may be further enhanced by addition to the thermoplastic ofadditional similar groups such as ethylene propylene rubber (EPR) whichis used as an impact modifier. In contrast, elastic films made withconventional diblock and/or triblock thermoplastic elastomers do notdevelop such good joint strength.

Shear strength is improved also by the use of increased numbers ofelastomer lanes of reduced size. For example, the shear strength offilms having a 2″ wide polyolefin lane and a ¼″ wide rubber lane weregreatly improved by reducing the lane widths to about ½″ and {fraction(1/16)}″ to ⅛″. Generally, rubber lanes that are of such narrowerdimension give much higher shear times. For example, a tape having asingle rubber lane may give a time of 1,000-2000 minutes. A tape of thesame material but with multiple more narrow lanes of rubber will yieldupwards of 10,000 to 20,000 minutes. Generally, the elastomer lane widthin a 3 to 8 mil thick film should be in the range of from about{fraction (1/16)}″ to ⅛″.

The foregoing improvement apparently relates to the division of work ofelasticity into two or possibly more lanes. This is believed to berelated to the facts that the propagation of a fracture due to thepresence of a cut or nick is pulling rate dependent and that stresseswithin an elastomeric lane that is failing are focused on a very smallportion of the elastomer. If there is only one elastomeric lane in thestretch zone of a tab that is being elongated, and that one lane has anick or cut, the stresses associated with said elongation are veryquickly focused on the point of crack propagation and complete failureoccurs in a short time. If there is a multiplicity of elastomeric lanes,only one of which has a cut or nick, the propagation of a crack acrossthe lane with the cut or nick is delayed because there are other,defect-free elastomeric lanes within the stretch portion of the tab thatcan accommodate the elongation without suffering failure. Ultimately, ofcourse, as elongation or pulling rate increases to very high values, atab will suffer failure, but at ordinary values the elastic responsetime of the defect-free lanes is short enough to substantially delayfailure in the lane that has a defect.

The end block reinforcing agents herein are of relatively high molecularweight, i.e. greater than 2000, as compared with prior art, and theyhave been found also to contribute to the improved caliper and rollconformation. Heretofore, coextrusion of adjacent elastic and nonelasticpolymer materials through a single die opening resulted in films havingsufficiently different thicknesses in the different polymer areas tocause nonuniform and unacceptable roll conformation. This resulted inlimited film widths that are commercially cost ineffective. For example,coextruded films in accordance with U.S. Pat. No. 4,787,897, supra, werefound to have undesirable caliper variation in the width directionyielding unacceptable roll conformation. That is, the rolls arenonuniform and have varying diameter dimensions along the axis of theroll and, for example, may have gauge bands of increased thicknessaround its circumference at the locations of the elastomeric lanes. Thegauge bands cause the elastomer to be distorted, which in turn, causesthe film to bunch-up and develop wrinkles upon unwinding, processing andre-winding the roll. The poor roll conformation significantly limits theroll width, e.g., to that of one or two diaper tape widths, which is notacceptable for commercial manufacture.

The arrangement and sizes of the elastomer and nonelastomer polymerareas have been found also to provide improvements in roll conformation.Generally, improvements in roll conformation have been achieved bylimiting the width of the elastomer portion. Also, improved rollconformation is achieved by providing increasing numbers of elastomerand nonelastomer portions of reduced size; i.e., an increased number oflaterally more narrow lanes. Roll conformation is improved also withoverall uniformity in the elastomer and nonelastomer arrangement acrossthe entire width of the sheet.

The film optionally includes one or two thin skins of polymer thatcompletely cover the adjacent lanes. That is, the distinct elastic andnonelastic polymer areas form substantially the entire thickness of thefilm, but a substantially thinner skin may be formed along one or bothof the film surfaces. Thermoplastic skins are preferred since they willgenerally have less surface friction and will aid machine processing ascompared with skins formed of thermoplastic elastomer. Also,thermoplastic skins will reduce, if not eliminate, the tendency of thefilm to block as by adherence of contacting elastomer lanes or polymerareas.

The thin film lowers the coefficient of friction on that side of thefilm on which it is present to provide handling advantages in webprocessing. The skin also provides a non-elastomeric surface on which tocoat an adhesive, and this may be of particular advantage if theadhesive or other coating is not inherently stable over time when coateddirectly onto the surface of thermoplastic elastomers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a disposable diaper having a tabfastener, waist band and leg cuff in accordance with the invention, withparts broken away;

FIG. 2 is a sectional view on an enlarged scale taken along the line 2—2in FIG. 1 showing that tab fastener in a deployed position;

FIG. 3 is a sectional view on an enlarged scale taken along the line 3—3in FIG. 1 showing the tab fastener in a storage position;

FIG. 4 is a sectional view on enlarged scale taken along the line 4—4 inFIG. 1;

FIG. 5 is a sectional view similar to FIG. 2 showing a two piece diaperfastening tape in accordance with the invention;

FIG. 6 is a fragmentary perspective view showing another embodiment of adisposable diaper in accordance with the invention;

FIG. 7 is a sectional view on an enlarged scale taken along the line 7—7in FIG. 6;

FIG. 8 is a schematic perspective view showing a coextrusion apparatusincluding a coextrusion die for making a flexible roll of film materialin accordance with the invention;

FIG. 9 is a cross-sectional view on an enlarged scale of the coextrusiondie shown in FIG. 8;

FIG. 10 is a perspective view of a die bar from the coextrusion die ofFIG. 9; and

FIG. 11 is a graphic representation of the lane widths of a coextrudedfilm material in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, there is shown a disposable diaper 10 in accordancewith the invention. The diaper 10 comprises a laminate or layeredassembly 12 having an inside surface 14 and an outside surface 16. Thediaper 10 has an hourglass configuration including a first end 18 and asecond end 20 connected by longitudinally extending edges 22 and 24.

The layered assembly 12 includes a liquid absorbent pad or batt core 26enclosed within a liquid permeable inner shell or top sheet 28 and aliquid impermeable outer shell or back sheet 30. The core 26 may be ofslightly smaller dimensions than the shells 28 and 30 so as to cause thelatter to form a perimeter or border about the core 26.

Referring to FIGS. 1, 2 and 3, the diaper 10 includes tab or tapefastener assemblies 32 secured to the first end 18 of the diaperadjacent associated longitudinal edges 22 and 24. The tabs 32 arearranged to provide side closure of the diaper 10 about an infant oruser upon engagement with landing member or zone 34. The landing member34 may comprise separate reinforcing tape members 34 a and 34 b as shownin solid outline or a single tape piece as shown by the combined solidand dotted outline in FIG. 1. As described in further detail below, thetabs 32 and landing member 34 may provide adhesive and/or mechanicalclosure of the diaper 10.

The tab 32 has a multilayer construction including a fastening elementor tape 36 having an outer face 38 and an opposed inner face 40. Thefastening tape 36 is secured to a release element or tape 42 having anouter face 44 and an inner face 46. The tapes 36 and 42 are assembledtogether in lengthwise alignment and adjacency in a conventional manner.

A proximal terminal end of the fastening tape 36 is secured by anadhesive layer 48 to the inner face 44 of the release tape 42. Apressure-sensitive adhesive layer 50 temporarily secures the distal endof the fastening tape 42 to the adjacent end of the release tape 42. Ina known manner, a silicone or carbamate release coat 52 may be appliedto the outer face 44 of the tape 42 to promote separation of theadhesive layer 50 and deployment of the fastening tape 36. The releasetape 42 is secured by an adhesive layer 54 to the adjacent longitudinaledge 22 of the diaper 10.

The fastening tape 36 includes a substrate or backing film 56 which isreversibly extensible. The substrate 56 includes alternating inelasticlanes 58 and elastic lanes 60. As shown, the alternating lanes extendthrough the entire thickness of the substrate 56. Various widths ofinelastic and elastic lanes may be selected, and the relative widths mayvary along the length of substrate 56.

As is customary, the tab 32 is cut in a machine cross direction from aroll of stock material. Accordingly, the length of the tab 32corresponds with the cross direction of the roll stock material and thewidth of the tab 32 corresponds with the machine direction of the rollstock. As explained more fully below, the alternating lanes 58 and 60are located at laterally spaced locations along the entire length of thetab 32 and extend across the full width thereof.

The elastic lanes 60 which contact adhesive 48 or 50 do not contributeto the elasticity of the tab during use. Even though the elasticproperty of such lanes is not taken advantage of, it has been discoveredthat positioning alternating lanes of inelastic and elastic materialacross the entire width of the roll stock material enhances the rollconformation, enabling higher quality, and high speed manufacture of thesame.

Referring to FIGS. 1 and 4, the diaper 10 includes a waist band 62secured to each of the diaper ends 18 and 20. The waist band 62 provideselastic characteristics and insures a tight fit of the diaper about theuser's waist. The waist bands 62 are secured to the longitudinal ends 18and 20 of the diaper 10 in any convenient manner including, for example,sonic welding or adhesives. The waist band 62 may be disposed betweenthe top sheet 28 and back sheet 30 of the diaper with appropriategathering or pleating of the sheets 28 and 30 to allow for expansion andcontraction of the diaper waist area.

Referring to FIG. 4, the waist band 62 is formed of a reversiblyextensible multilayer film 64 having a core portion 66 formed ofalternating elongate inelastic lanes or stripes 68 and elastic lanes orstripes 70. The film 64 includes opposed skins 72 and 74 extending alongopposite surfaces thereof. (The thicknesses of the skins 72 and 74 aregreatly exaggerated in FIG. 4.) The skins 72 and 74 may be formed of thesame polymer as the inelastic lanes 68. The skins 72 and 74 provide thewaist band 62 with a smooth exterior that is comfortable upon contactwith the user's skin.

The skins 72 and 74 have little or no affect on the reversibleextensible character of the film 64. That is, the films 72 and 74 maysimply fail or permanently distort upon elongation of the film 64 withlittle or no user perceptible difference in the stress and strainproperties.

Referring to FIG. 1, the diaper 10 includes leg cuffs 76 secured to thelongitudinal edges 22 and 24 of the diaper. The leg cuffs 76 may beformed of the same film 64 as the waist band 62. The leg cuffs 76 aredisposed between the top sheet 28 and back sheet 30 of the diaper. Thetop and back sheets 28 and 30 are gathered or pleated in a known mannerto allow for the elastic extension and contraction of the longitudinaledges of the diaper in the leg cuff region.

For convenience of illustration, the tabs 32, waist bands 62 and legcuffs 76 are included in the diaper 10. Of course, any one orcombination of these features may be used in a diaper in accordance withthe invention.

A modified tab in accordance with the invention is shown in FIG. 5. Forconvenience, modified elements are identified with the same referencenumeral with the addition of a prime designation.

Referring to FIG. 5, a two piece tab or fastener assembly 32′ includes amodified release tape 42′ that is mounted onto the inside surface 14 ofthe diaper 10. The fastening tape 36 is identical to that describedabove, but it is mounted directly to the outside surface 16 of thediaper 10. The outboard end of the release tape 42′ extends onto theinside face 40 of the tape 36, and the adhesive layers 54′ and 48′ maybe joined to improve the Y-bond strength. As in the first embodiment,the tape 36 includes a plurality of elastic lanes 60 that are fixed aspart of the factory joint.

Referring to FIG. 6, a diaper 10′ in accordance with another embodimentof the present invention is shown. For convenience, correspondingelements are identified with the same reference numeral as in the firstembodiment with the addition of a prime designation.

The diaper 10′ includes a stretchable ear or wing 80 mounted adjacentthe longitudinal edge 24′ of the diaper end 18′. The wing 80 is securedto the longitudinal edge 24′ of the diaper in any convenient manner, forexample, sonic welding or adhesives. A similar wing (not shown) ismounted adjacent to longitudinal edge 22′. The stretchable wingarrangement provides waist tension and an elastic waist band isgenerally not necessary.

The diaper 10′ includes a mechanical fastener arrangement comprising ahook tab 82 and a landing zone loop tab 84. Of course, any of the knownmechanical fastener elements may be used to provide the fastenerarrangement. As indicated above, the first embodiment may have a similarmechanical fastener instead of the illustrated adhesive fastener.

Referring to FIG. 7, the hook tab 82 includes an inelastic substrate 86having hook members 88 projecting therefrom for engagement with the looptab 84. The hook tab substrate 86 is secured to the wing 80 by anadhesive layer 90 or in another suitable manner.

The wing 80 is formed of a film 92 having alternate inelastic portions94 and elastic portions 96. The film 92 includes a skin 98 extendingalong only one surface. The skin 98 may be formed of the same polymerforming the inelastic portions 94.

Referring to FIG. 8, a coextrusion apparatus 100 which may be used tomake the films 56, 64 and 92 in accordance with the invention is shown.This apparatus is described in greater detail in U.S. Pat. No.4,435,141, the teachings of the patent being incorporated by reference.

Suitable polymer charges for forming inelastic and elastic films orlanes are respectively supplied to melt screw extruders 102 and 104. Thepolymer charges are melted in the extruders 102 and 104, and the moltenpolymers are forced at a predetermined pressure and temperature throughlines 106 and 108 to a coextrusion die 110.

The polymer charges are heated to temperatures that sufficiently reducethe polymer viscosity to allow transportation and extrusion. Theextrusion temperatures do not exceed that which would result in thermaldegradation of the polymers.

A confluence of the molten polymers is extruded as a multilayer andmulti-component film 112. The film 112 may be contacted with a castingroll (not shown) for initial cooling and further processed in aconventional manner. Although it is not part of the extrusion process,the film 112 may be pattern coated with adhesive in a known manner atadhesive coating station “S”. For example, adhesive layers 48 and 50 maybe applied at spaced locations along the width of the film 112.

Referring to FIG. 9, a cross-sectional view of the coextrusion die 110is shown. The coextrusion die 110 includes an elongate body member 118and a similarly elongate die bar 120. The die 110 may itself comprise abody block 122 and two opposing body sections 124 and 126. The opposingbody sections 124 and 126 may be held to the body block 122 by aplurality of bolts 128.

The body block 122 may be formed with first and second conduits 130 and132 (shown in dotted outline) for respectively conducting a moltenthermoplastic polymer feed to a manifold 134 and a molten thermoplasticelastomer feed to a manifold 136.

The body section 124 is formed with a manifold surface 138 forcooperating with a surface 140 of the body block 122 to form a firstmanifold for longitudinally distributing the thermoplastic polymer feed.In a similar manner, body section 126 is formed with a manifold surface142 that cooperates with another manifold surface 144 of the body block122 to form a second manifold for longitudinally distributing thethermoplastic elastomer.

The body sections 124 and 126 cooperate to define a passage 146 forconducting the confluence of the polymers to an elongate die opening148. The die opening 148 is defined by the adjacent lip portions 150 and152 provided by the opposed body portions 124 and 126. The size of thedie opening 148 may be adjusted by operation of screw 154.

Referring to FIG. 10, the die bar 120 includes intersecting die barfaces 156 and 158. The faces 156 and 158 intersect at a common notchededge 160. Projections 162 and 164 are formed in each of the faces 156and 158. The projections 162 and 164 split the flow of polymer chargefrom associated manifolds 134 and 136 into separate streams which areinterspersed adjacent to the edge 160 to form the coextruded film 112with alternate lanes or stripes of the polymers. The projections 162 and164 may be sized and spaced along the surfaces 156 and 158 to providedesired patterns and lane widths.

The film may be provided with a continuous skin on one or both surfacesthereof by means of inserting a shim between the body block 122 and oneor both of the body sections 124 and 126. A shim 166 is shown in dottedoutline disposed between the body block 122 and the body section 124.The shim 166 causes a thermoplastic skin to be formed on one surface ofthe film 112. The skin thickness may be varied by use of shims ofsuitable thicknesses.

Referring to FIG. 11, a graphic representation of a repeating array oflane widths for roll stock of film material, such as film 112, is shown.The illustrated lane widths are selected for use in the manufacture ofdiaper tapes, such as the fastening tape 36 of the tab 32.

In this example, the fastening tape 36 has a total length of 75 mmextending in the cross direction of the roll stock. The intended diaperattachment locations or allocated cross direction extents in accordancewith the functions of the various portions of the fastening tape in adiaper application are indicated in FIG. 11.

Accordingly, a first terminal segment or factory joint portion of thediaper tape to be secured to the diaper back sheet 30 (directly or via arelease tape) includes two inelastic lanes and a center elastic lane.This back sheet portion of the fastening tape will be coated with asuitable adhesive, e.g. adhesive 48 at station S in FIG. 8, forpermanent attachment to the diaper 10.

The central stretch segment or portion of the fastening tape includes acentral inelastic lane disposed between two elastic lanes. An inelasticlane is provided at each of the extremities of the stretch portion. Thetwo elastic lanes provide substantially all of the tape elasticity orstretch in the diaper application. of course, other combinations oflanes and lane types may be used.

The second terminal segment or landing zone portion of the tape containsan array of elastic and inelastic lanes similar to that used in thestretch portion. The landing zone portion of the tape is slightly largerthan the stretch portion, and it is intended to be positioned on thelanding zone of the diaper for engagement therewith. Accordingly, thesecond terminal segment or landing zone portion of the tape may becoated with a suitable adhesive, e.g. adhesive layer 50 at station S inFIG. 8, or provided with a mechanical fastener for diaper closure.

The film edge of the roll stock material is shown at the left in FIG.11, and the slit line is shown at the right. It should be appreciatedthat the fastening tape array shown in FIG. 11 may be repeated manytimes across the full width of the film material of the roll stock. Forexample, the array will be repeated 20 times for 1500 mm wide roll stockmaterial.

The following films were prepared using a coextrusion apparatus asdescribed above and alternating inelastic and elastic lanes as shown inFIG. 11. The thermoplastic elastomers used to make the elastic lanes areidentified in Table 1 together with the end blocking resin, if added.The inelastic lanes were formed of PROFAX 8523, a high impactpolypropylene supplied by Montell USA. The polymers were charged to thecoextrusion apparatus and the films were coextruded at variousthicknesses. The roll stock material had a width of about 20 inches or508 mm, and in many cases acceptable roll conformation was obtained inthese cases. (At 60 inches or 1500 mm roll width, similar or betterresults are obtained.) However, preferred results were obtained with thetetrablock elastomers having an end block reinforcing resin. Diaper tabswere cut in the cross direction from the films to prepare examples 1-27.

TABLE 1 Example No. Rubber Polymer Endblocking Resin RATIO 1  GRP 6906¹¹— — 2 GRP 6906  CUMAR LX 509² 96/4 3 GRP 6906 CUMAR LX 509 92/8 4 GRP6906 CUMAR LX 509 88/12 5  G1730³ — — 6 G1730 BHPP 820⁴ 97/3 7 G1730CUMAR LX 509 96/4 8 G1730 CUMAR LX 509 92/8 9 G1730 CUMAR LX 509 88/1210 G1730 CUMAR LX 509 75/25 11 G1730  PPE⁵ 97/3 12 G1730 PPE 97/3 13G1730 EXXACT 4033⁶ 80/20 14 GRP 6906 EXXACT 3128⁷ 80/20 15  SEPTON 2043⁸— — 16 SEPTON 2043 CUMAR LX 509 92/8 17 SEPTON 2043 CUMAR LX 509 82/1618  SEPTON 2063⁹ — — 19 GRP 6906 — — 20 G1730 CUMAR LX 509 80/20 21G6906 CUMAR LX 509 90/10 22 G1730 CUMAR LX 509 80/20 23 G6906 — — 24G6906 — — 25 G1730 — — 26 G6906 CUMAR LX 509 90/10 27  G1652¹⁰ EPR¹¹95/5 ¹GRP 6906 is a styrene/ethylene-propylene/styrene triblock polymersold by Shell Chemical Company. ²CUMAR LX 509 is a coumarone-indeneresin used as an end block reinforcing resin herein, sold by NevilleChemical Company. ³G1730 is a SEPSEPstyrene/ethylene-propylene/styrene/ethylene-propylene tetra blockcopolymer sold by Shell Chemical Company. ⁴BHPP 820 is a polyphenylether resin having a molecular weight of 36,000 used as an end blockreinforcing resin herein, sold by General Electric Company. ⁵PPE is apolyphenyl ether resin having a molecular weight of 4,000 used as an endblock reinforcing resin herein. ⁶EXXACT 4033 is a metallocene plastomercomprising a high density rubbery polyolefin used herein as an end blockreinforcing resin, sold by Exxon. ⁷EXXACT 3128 is a metalloceneplastomer comprising a low density rubbery polyolefin that blends withthe rubber, sold by Exxon. ⁸SEPTON 2043 is a SEPSstyrene/ethylene-propylene/styrene triblock polymer, sold by KurarayChemical of Japan. ⁹SEPTON 2063 is a SEPSstyrene/ethylene-propylene/styrene triblock polymer, sold by KurarayChemical of Japan. ¹⁰G1652 is a SEBS styrene/ethylene-butylene/styrenetriblock copolymer sold by Shell Chemical Company. ^(11.)EPR is anethylene-propylene copolymer rubber having a grade designation EPM 306,that blends with the rubber, sold by Bayer.

The calipers and widths of the diaper tabs of examples 1-27 weremeasured and the results are reported in Table 2 below. The end blockreinforcing agents enabled thicknesses ranging from 3 to 8.5 mils asmeasured in the elastic or rubber portions of the films.

The shear strengths of the diaper tabs of examples 1-27 were measured ina lengthwise direction at 100° F. using a 500 gram static shear load.The area of the elastic or rubber portions of each tab between the testjaw and the applied static load was measured. The static load wasallowed to hang until the tab failed. Three samples were tested in eachcase, and the average times to failure are reported in minutes. Theelastic area was substantially identical for each of the three samplesof each example, and a single rubber area is reported.

In order to relate the failure time to the elastic or rubber portion ofthe film, the ratio of (1) the average minutes to failure to (2) theelastic or rubber cross-sectional area is reported as a normalized shearvalue.

TABLE 2 Ex- Elas- Elastomer Shear am- tomer Cross-Sectional (normalizedto ple Caliper Width Area Shear unit cross- No. (mils) (inches) (mils²/1in. tab) (Minutes) sectional area) 1 4.8 ½ 2400 290 0.1207 2 4.4 ⅝ 2750442 0.1608 3 4 ⅜ 1500 1224 0.8160 4 4.4 ⅜ 1650 2718 1.6473 5 4.6 ¼ 1150208 0.1806 6 4 {fraction (7/32)} 876 89 0.1020 7 4.5 {fraction (6/32)}846 719 0.8495 8 4.3 {fraction (7/32)} 942 780 0.8277 9 4.3 {fraction(10/32)} 1344 4175 3.1064 10 4.8 {fraction (7/32)} 1051 4175 3.9724 11 7{fraction (11/32)} 2406 1563 0.6496 12 3 {fraction (10/32)} 936 1770.1891 13 3.5 {fraction (7/32)} 766 70 0.0914 14 5.2 {fraction (11/32)}1789 5429 3.0345 15 3.6 {fraction (11/32)} 1238 70 0.0565 16 6.3{fraction (5/32)} 983 1295 1.3174 17 8.5 {fraction (4/32)} 1062 54875.1667 18 6.4 {fraction (4/32)} 800 97 0.1208 19 4 {fraction (11/32)}1376 417 0.3031 20 3.2 {fraction (15/32)} 1500 354 0.2358 21 4 {fraction(11/32)} 1376 153 0.1114 22 3 {fraction (15/32)} 1407 305 0.2165 23 6{fraction (4/32)} 750 681 0.9076 24 5.6 {fraction (9/32)} 1574 4080.2594 25 3.8 {fraction (10/32)} 1186 107 0.0905 26 8.3 {fraction(7/32)} 1818 2718 1.4950 27 8 {fraction (9/32)} 2248 1 0.0006

The mode of shear failure of the examples is related to the relativestrength of the joint. The tetrablock elastomers typically result infailure occurring within the rubber as opposed to at the joint. On theother hand, the triblock elastomers also tend to fail in the rubber, butthere are limited occurrences of joint failure. It should be appreciatedthat the inelastic or polyolefin may be combined or modified to increaseits compatibility with the rubber or elastomers as by incorporation ofsimilar hydrocarbon components, e.g. ethylene-propylene.

A most important factor in the improvements in joint strength is thetype of elastic polymer or rubber used. For example, SI, SIS, SB, SBS,SEB, SEBS, SEP and SEPS thermoplastic elastomers were tested incombination with a polyolefin. (The foregoing letter notations are usedin a conventional manner to identify polymer blocks with S beingstyrene, I being isoprene, B being butylene, EB being ethylene-butyleneand EP being ethylene-propylene.) The following resulted:

SI(S) rubbers have poor joint strength and degrade in a short time attypical polyolefin extrusion temperatures;

SB(S) rubbers exhibit better joint strengths than SI(S), but not as goodas SEPSEP;

SB(S) rubbers have the highly undesirable property of cross linking onexposure to polyolefin extrusion temperatures; and

SEB(S) rubbers have good stability at polyolefin extrusion temperaturesand joint strengths better than SI(S), but not as good as SEPSEP.

Only when the thermoplastic elastomer contained SEPSEP tetrablockelastomer was it observed that superior joint strength and uniform, aswell as low calipers, were achieved. These improvements over triblockare believed to be related to several factors. Firstly, the tetrablockpolymer has a lower viscosity than a triblock of similar molecularweight, and the tetrablock polymer softens and breaks-up at a lowertemperature than triblock polymer. This results in an elastomer withbetter melt extrusion properties. Secondly, one end of the fourth (D)block, the “tail” of the polymer, is not tied to an immobile styreneendblock and it therefore has greater molecular mobility than a midblock(B) which is tied at both ends to a styrene block. This greater mobilityallows the tail to more freely associate with molecules such as the EPRimpact modifier in a polypropylene resin and ultimately leads to a moreintimate bond between the elastomer lane and thermoplastic lane than ispossible with the triblock-based elastomer.

Herein, a tetrablock polymer with ethylene-propylene rubber segments isfavored. For example, KRATON G1730 is a SEPSEP block polymer containingabout 19 to 21 percent styrene by weight, the styrene blocks having amolecular weight of about 12,000. The styrene blocks give the rubber itsthermoplastic character and strength. The styrene blocks are connectedby the ethylene-propylene blocks. The ethylene-propylene block isbelieved to impart rubbery characteristics to the polyolefin and/orinhibit crystallization. The ethylene-propylene block is also believedto inhibit fracture propagation and improve flex characteristics. Theterminal ethylene-propylene block provides a tail-like extension beyondthe adjacent styrene.

It is observed that there is no distinct boundary between the polyolefinand SEPSEP elastomer when the joint is stretched in a transversedirection. The polyolefin and the elastomer appear to blend together atthe joint, and this is believed to be due to the similarity in structureof the polyolefin and the ethylene propylene tail of the tetrablockwhich in turn is believed to give the good joint strength.

The joint strength is sufficiently good that a typical tensile testshows elongation of the polypropylene before the joint separates. Also,in such a tensile test, the polypropylene begins to neck down inthickness immediately adjacent to the joint prior to failure. (Theelastomer is still at its extruded thickness.) The joint may not bestronger than the polypropylene in bulk or on average, but it appears tobe stronger than the polypropylene in the neck down thickness portion.In typical tensile tests pulling a one inch wide tab at 20 inches perminute, the polypropylene breaks before the joint. The joint exceeds thestrength of the polypropylene since the polypropylene yields withoutjoint failure.

The boundary between the polyolefin and elastomer lanes is not planar,but rather, it typically has an oval cross-sectional shape as indicatedin FIG. 4. The elastomer may have any elongated or flattened oval shapecross-section. Specific cross-sectional shapes depend upon the selectionof rubber and polyolefin.

The improvements in high temperature shear strength are believed to beassociated with the interaction of the end block reinforcing agent andthe end block of the rubber. When end block reinforcing agents are mixedwith SIS, SB or SEP rubbers they associate with the end block, enlargeit and help to give it cohesive strength. The end block of styrene in arubber block polymer may have a molecular weight of from 10,000 to20,000. Addition of an end block reinforcing agent may change the totalmass of that styrene block to 40,000.

The end block reinforcing agent may also improve the crystallinecharacter of the styrene end block of the rubber and thereby raise itsmelting temperature. Of course, other additives having a relativelyhigher melting temperature than the end block increase the averagemelting temperature through physical mixture and average molecularweight increases.

The relative amount of the reinforcing end block agent affects therelative calipers of the polyolefin and elastomer. More particularly, arelatively higher molecular weight styrene block causes increased dieswell during extrusion and an increased final film gauge in theelastomer or rubber area. For example, a test of the polymers in theU.S. Pat. No. 4,787,897, supra, without reinforcing resins resulted in alarge amount of die swell. This is believed to be due to be largestyrene blocks in the triblock polymers used in the '897 patent. Largestyrene blocks swell and make it extremely difficult to extrude a flatfilm. Consequently, the films had large bulges where the rubber lanesare located.

The tetrablock polymers have smaller end blocks, and when coextruded byitself, it comes out about half as thick as the polypropylene. Uponaddition of a small amount of reinforcing resin to improve the elevatedtemperature shear, it was found to be just about the amount needed tocause rubber to extrude at the same caliber as the polypropylene.ENDEX-160, a polycyclic arene reinforcing agent sold by Hercules havinga softening point of 160° C., can be used at levels of 5 to 25 percentby weight. At 14% resin and 86% rubber, the elastomer is thicker thanpolyolefin, but at 8% resin and 92% rubber, the elastomer is thinnerthan polyolefin. Accordingly, somewhere in the middle of that rangethere is an optimum.

The optimum for shear strength is actually a little higher than 14percent, and it does not coincide with the optimum uniform caliper.However, somewhere in the window, sufficient shear strength is achievedfor diaper tape applications. Similarly, optimum formulations for otherapplications may be determined quickly with routine trial and errorsampling techniques.

Another advantage of the KRATON G1730 tetrablock rubber is that at orabout the amount that gives uniform extrusion properties as betweenpolyolefin and rubber as well as good elevated temperature shear, theresulting elasticity or stress/strain character is substantially equalto that desired in a diaper tab. A preferred diaper tab elasticity is3.5 lbs. force for a 1″ wide tab at 100% elongation.

Using coextrusion apparatus as shown in FIGS. 7-9 to make apolypropylene and SEPSEP roll of film stock material having a 1500mm or60 inch width, the film thickness was measured at each elastic laneacross the film width. The skin was continuous and varied in thicknessfrom about 7 microns to about 25 microns. The thin skin is believed tobe due in part to the compatibility between the rubber and thepolyolefin, with the skin tending to diffuse into the rubber. The skinprovides only the slightest deviation in stress/strain testing.

In the foregoing film, the thicknesses of the rubber lanes varied fromabout 180 microns to about 250 microns across the film width. Thealternate lanes of polypropylene were of thicknesses similar to those ofthe rubber lanes. Relatively thin films, e.g. 3 mils or less, arepossible with the use of the tetrablock polymers and end blockreinforcing agents in accordance with the invention. In comparison, theteachings of U.S. Pat. No. 4,787,897, supra, did not enable productionof films less than about 8 to 12 mils in thickness.

The invention is not restricted to the slavish imitation of each andevery detail set forth above. Obviously, devices may be provided whichchange, eliminate, or add certain specific details without departingfrom the invention.

What is claimed:
 1. A construction film comprising a coextrusion ofadjacent elastic lanes and inelastic lanes for use in making areversibly extensible stretchable film including a stretch zone which istensioned by sheer loads during use of the stretchable film, saidconstruction film having a machine direction and a cross direction withsaid lanes being laterally spaced in said cross direction andlongitudinally parallel in said machine direction, said stretchable filmbeing formed from said construction film so that said stretchable filmhas a length extending in the cross direction and a width extending inthe machine direction of said construction film, said inelastic lanesbeing formed of a thermoplastic polymer and said elastic lanes beingformed of a thermoplastic elastomer, said stretchable film and saidconstruction film lanes being dimensioned so that said stretchable filmhas at least two spaced elastic lanes extending across the width of saidstretchable film within said stretch zone to distribute shear loadsapplied to said stretchable film and inhibit propagation of tearingfailures, said thermoplastic elastomer comprising a block polymer ofmolecules having rubbery segments and non-rubbery segments, said blockpolymer including terminal end segments formed of said rubbery segments.2. The film of claim 1, wherein said rubbery segment includesethylene-propylene.
 3. The film of claim 2, wherein said non-rubberysegment is selected from the group consisting of substituted andunsubstituted vinyl arenes.
 4. The film of claim 1, wherein said blockpolymer has a tetrablock ABAD structure wherein A is selected from thegroup consisting of styrene and alkyl substituted styrene, and B and D,which may be the same or different, comprise conjugated dienes.
 5. Thefilm of claim 4, wherein said block polymer is a SEPSEP tetrablockpolymer.
 6. The film of claim 5, wherein said stretchable film has athickness in the range of from about 3 to about 10 mils, said elasticand inelastic lanes have substantially equal thicknesses, said inelasticlane has a width in the range of from about {fraction (1/16)} to 2.0inches and said elastic lane has a width of from about {fraction (1/16)}to about 1.0 inch.
 7. The film of claim 1, wherein an aromatic end blockreinforcing resin is added to said thermoplastic elastomer in an amountequal to from about 5 percent to about 25 percent based on the weight ofsaid thermoplastic elastomer.
 8. The film of claim 1, wherein anaromatic end block reinforcing resin is added to said thermoplasticelastomer in an amount sufficient to increase the elevated temperatureshear strength and to cause said elastic and inelastic lanes to be ofsubstantially equal thickness.
 9. The film of claim 8, wherein said endblock reinforcing resin is selected from the group consisting ofpolyphenylene oxides and polycyclic arenes.
 10. The film of claim 1,wherein said stretchable film also includes at least one skin layer ofsaid thermoplastic polymer that substantially covers said elastic lanes.11. The film of claim 10, wherein said skin layer substantially coverssaid adjacent elastic and inelastic lanes.
 12. The film of claim 1,wherein said stretchable film includes a thin skin layer of polymer oneach side thereof.
 13. The film of claim 1, wherein said constructionfilm is provided in rolls as a roll stock material, said stretchablefilm also includes at least one mounting zone that is not intended tostretch, said mounting zone being connected to said stretch zone, and atleast a third of said elastic lanes extends across the width of saidstretchable film within said mounting zone to increase the uniformity ofthe distribution of alternating elastic and inelastic lanes in the crossdirection of said roll stock material and to thereby improve rollconformation of said roll stock material.
 14. The film of claim 1,wherein said stretchable film comprises an element of a member selectedfrom the group consisting of tapes, waist bands, leg cuffs and tensionapplying multiple flexible films.
 15. The film of claim 1, wherein saidstretchable film is a fastening tape and said stretch zone is a centralportion of said fastening tape connecting opposed terminal end portions,said terminal end portions being sized to secure said fastening tape toform a tensioned closure with said central portion providing elasticity,said central portion including said at least two of said elastic lanesto increase said tape's resistance to shear failure as compared with asimilar tape having a single elastic lane.
 16. The film of claim 15,wherein said fastening tape has a length, said construction film crossdirection is at least several times greater than said fastening tapelength, said construction film has allocated cross direction extentscorresponding with said terminal portions of said tape, and saidallocated cross direction extents include elastic lanes to improve rollconformation of said construction film.
 17. The film of claim 16,wherein said block polymer has a tetrablock ABAD structure wherein A isselected from the group consisting of styrene and alkyl substitutedstyrene, and B and D, which may be the same or different, compriseconjugated dienes.
 18. The film of claim 17, wherein said fastening tapehas a thickness in the range of from about 3 to about 10 mils, saidelastic and inelastic lanes have substantially equal thicknesses, saidinelastic lane has a width in the range of from about {fraction (1/16)}to 2.0 inches and said elastic lane has a width of from about {fraction(1/16)} to about 1.0 inch.
 19. The film of claim 18, wherein an aromaticend block reinforcing resin is added to said thermoplastic elastomer toincrease elevated temperature shear strength to resist a 500 g shearload for more than 1000 minutes at 100° F.
 20. The film of claim 19,wherein said end block reinforcing resin is selected from the groupconsisting of polyphenylene oxides and polycyclic arenes.
 21. A methodof making roll stock material having a machine direction and a crossdirection for use in making a reversibly extensible stretchable filmincluding a stretch zone which is tensioned by sheer loads during use ofthe stretchable film, said stretchable film having a length and a width,comprising providing first and second charges of film-forming polymer,said first charge comprising a thermoplastic elastomer and said secondcharge comprising a thermoplastic polymer, coextruding said charges offilm-forming polymer to form said roll stock material with alternateelastic lanes formed of said thermoplastic elastomer and inelastic lanesformed of said thermoplastic, said lanes being integrally joined andextending in said machine direction, forming said stretchable film withits length and width extending respectively in the cross direction andthe machine direction of said roll stock material, and sizing saidstretchable film and said lanes so that said stretchable film has atleast two spaced elastic lanes extending across the width of saidstretchable film within said stretch zone to distribute shear loadsapplied to said stretchable film and inhibit propagation of tearingfailures, said thermoplastic elastomer comprising a block polymer ofmolecules having rubbery segments and non-rubbery segments, said blockpolymer including terminal end segments formed of said rubbery segments.22. The method of claim 21, wherein said elastic lane has a width offrom about {fraction (1/16)} to about 1.0 inch and said inelastic lanehas a width in the range of from about {fraction (1/16)} to 2.0 inches.23. The method of claim 22, wherein said stretchable film includes atleast one mounting zone that is not intended to stretch, said stretchzone being connected to said stretch zone, and at least a third of saidelastic lanes extends across the width of said stretchable film withinsaid mounting zone to increase the uniformity of the distribution ofalternating elastic and inelastic lanes in the cross direction of saidroll stock material and to thereby improve roll conformation of saidroll stock material.
 24. The method of claim 23, wherein said blockpolymer is a tetrablock polymer of ABAD structure wherein A is a vinylaromatic hydrocarbon polymer block, and B and D are conjugated dienepolymer blocks.
 25. The method of claim 23, wherein said block polymeris a tetrablock polymer of ABAD structure wherein A is selected from thegroup consisting of styrene and alkyl substituted styrene, and B and D,which may be the same or different, are selected from the groupconsisting of hydrogenated butadiene polymer block, hydrogenatedethylene-propylene and hydrogenated isoprene polymer block.
 26. Themethod of claim 25, wherein an aromatic end block reinforcing resin isadded to said charge of block polymer to increase the elevatedtemperature shear strength of said thermoplastic elastomer and to moreclosely conform extruded thicknesses of said thermoplastic elastomer andthermoplastic polymer.
 27. The method of claim 26, wherein said aromaticend block reinforcing resin is selected from the group consisting ofpolyphenylene oxides and polycyclic arenes.
 28. The method of claim 26,wherein said roll stock material includes at least one skin layer ofsaid thermoplastic polymer.
 29. A construction film comprising acoextrusion of adjacent elastic lanes and inelastic lanes for use inmaking a reversibly extensible stretchable film, said construction filmhaving a machine direction and a cross direction with said lanes beinglaterally spaced in said cross direction and longitudinally parallel insaid machine direction, said stretchable film being formed from saidconstruction film so that said stretchable film has a length and a widthrespectively extending in the cross direction and the machine directionof said construction film, said inelastic lanes being formed of athermoplastic polymer and said elastic lanes being formed of atetrablock thermoplastic elastomer, said tetrablock thermoplasticelastomer having rubbery segments and non-rubbery segments, saidtetrablock thermoplastic elastomer having a terminal end formed of saidrubbery segments.
 30. The film of claim 29, wherein said rubbery segmentincludes ethylene-propylene groups.
 31. The film of claim 30, whereinsaid non-rubbery segment is selected from the group consisting ofsubstituted and unsubstituted vinyl arenes.
 32. The film of claim 29,wherein said tetrablock thermoplastic elastomer has an ABAD structurewherein A selected from the group consisting of styrene and alkylsubstituted styrene, and B and D, which may be the same or different,comprise conjugated dienes.
 33. The film of claim 29, wherein saidtetrablock thermoplastic elastomer has an ABAD structure wherein A isselected from the group consisting of styrene and alkyl substitutedstyrene, and B and D, which may be the same or different, are selectedfrom the group consisting of hydrogenated butadiene polymer block,hydrogenated ethylene-propylene and hydrogenated isoprene polymer block.34. The film of claim 29, wherein said tetrablock thermoplasticelastomer is SEPSEP tetrablock polymer.
 35. The film of claim 29,wherein an aromatic end block reinforcing resin is added to saidthermoplastic elastomer in an amount equal to from about 5 percent toabout 25 percent based on the total weight of said resin and polymer.36. The film of claim 29, wherein an aromatic end block reinforcingresin is added to said thermoplastic elastomer in an amount sufficientto increase the elevated temperature shear strength and to cause saidelastic and inelastic lanes to be of substantially equal thickness. 37.The film of claim 36, wherein said end block reinforcing resin isselected from the group consisting of polyphenylene oxides andpolycyclic arenes.
 38. The film of claim 29, wherein said stretchablefilm also includes at least one skin layer of said thermoplastic polymerthat substantially covers said elastic lanes.
 39. A construction filmcomprising a coextrusion of adjacent elastic lanes and inelastic lanesfor use in making a reversibly extensible stretchable film including astretch zone which is tensioned by sheer loads during use of thestretchable film, said construction film having a machine direction anda cross direction with said lanes being laterally spaced in said crossdirection and longitudinally parallel in said machine direction, saidstretchable film being formed from said construction film so that saidstretchable film has a length extending in the cross direction and awidth extending in the machine direction of said construction film, saidinelastic lanes being formed of a thermoplastic polymer and said elasticlanes being formed of a thermoplastic elastomer, said thermoplasticelastomer having an aromatic end block reinforcing resin added to it inan amount equal to from about 5 percent to about 25 percent based on theweight of said thermoplastic elastomer, said reinforcing resin having amolecular weight greater than 2000, said stretchable film and saidconstruction film lanes being dimensioned so that said stretchable filmhas at least two spaced elastic lanes extending across the width of saidstretchable film within said stretch zone to distribute shear loadsapplied to said stretchable film and inhibit propagation of tearingfailures.
 40. A construction film comprising a coextrusion of adjacentelastic lanes and inelastic lanes for use in making a reversiblyextensible stretchable film including a stretch zone which is tensionedby sheer loads during use of the stretchable film, said constructionfilm having a machine direction and a cross direction with said lanesbeing laterally spaced in said cross direction and longitudinallyparallel in said machine direction, said stretchable film being formedfrom said construction film so that said stretchable film has a lengthextending in the cross direction and a width extending in the machinedirection of said construction film, said inelastic lanes being formedof a thermoplastic polymer and said elastic lanes being formed of athermoplastic elastomer, said stretchable film and said constructionfilm lanes being dimensioned so that said stretchable film has at leasttwo spaced elastic lanes extending across the width of said stretchablefilm within said stretch zone to distribute shear loads applied to saidstretchable film and inhibit propagation of tearing failures, saidconstruction film being free of coextrusion processing aid resins havinga molecular weight of less than 2000 or a softening point less than 80°C.